This invention relates generally to pressure transducers and more particularly to such transducers using strain gauge technology for sensing pressure change to produce an electrical signal related to such change and employing electronics for processing and amplifying the signal.
Although the use of strain gauge technology for converting changes in fluid pressure to related electrical signals is known, there exists a need to provide transducers which are more easily manufacturable and which have improved reliability. There is also a need to minimize the cost of producing the transducers so as to make it more economically feasible to use them in given applications and thus increase manufacturing volume with resulting savings in large volume manufacturing techniques. For example, strain gauge technology involves the use of type 17-4 stainless steel for the diaphragm member exposed to the pressure being monitored; however, this material is relatively expensive and is difficult to machine so that it is desirable to design components which need to be formed of such material so that a minimum amount of material, machining time and waste material are involved. Another problem relates to the use of O-ring seals due to the difficulty in maintaining uniformity in the sealing surfaces during the crimping process.
With regard to making electrical connections among the transducer terminals, electronic components and sensor elements, typically one or more intermediate connection components have been used which involve soldering of individual components, as well as intermediate connections, with each soldering operation increasing a failure possibility and decreasing reliability. Strain gauge technology also involves the use of wire bonds between the strain gauge sensor elements and the transducer circuits and, if flexible circuits are employed, the problem that ultrasonic bonding occasions due to the associated vibration militates against obtaining reliable connections to a flexible circuit and toward using an intermediate connection device which again adds a process step and potential failure points.
It is an object of the present invention to provide a pressure transducer which has improved reliability and yet is relatively low in cost. Yet another object is the provision of a pressure transducer not subject to the prior art limitations noted above. Yet another object of the invention is the provision of an improved method for assembling an electronic package which incorporates a flexible circuit assembly.
Briefly described, in accordance with the invention, a tubular port fitting having a fluid receiving opening at one end and a closed, integrally formed diaphragm at an opposite pedestal end has an angular orientation feature and a locking feature for locking receipt of a support member in a selected angular orientation on the pedestal end. The support member has an apertured flat end wall surface received on the diaphragm portion, the aperture being in alignment with strain gauge sensor elements glass bonded to the diaphragm portion. A flexible circuit assembly has a first lobe section for mounting electronic components including an integrated circuit; the lobe section bonded to the rigid, flat end surface of the support with an opening aligned with the aperture in the flat surface. A second lobe section of the flexible circuit assembly is placed on a seating surface of an adjacent inverted connector held at an optimum level relative to the flat end wall surface, the connector having terminals with free distal ends extending into an electronics chamber in which the seating surface is disposed. The free distal ends are received through apertures in the second lobe section and soldered to respective circuit pads on the second lobe section along with soldering of electronic components on selected portions of the flexible circuit assembly. Wires are then ultrasonically bonded both to the strain gauge sensor elements and to circuit pads on the bonded lobe section of the flexible circuit assembly and then encapsulated by silicone gel.
According to a feature of a first embodiment, a cup-shaped EMC shield is received in the connector""s electronics chamber, the shield provided with tabs which extend outwardly through openings in the connector""s side wall beyond the outer periphery of the connector""s walls. The connector is then turned over with an intermediate portion of the flexible circuit assembly extending between the lobe sections bent into a generally U-shape configuration and with wall portions of the connector locking onto the support member. According to a feature of the first embodiment, a radially extending mounting flange is hermetically welded to the port fitting and a hexagonal metal housing member is received over the body of the connector with the EMC shield tabs spring biased into electrical connection with the housing member and with the housing member applying a selected load to an O-ring placed in a circumferentially extending groove formed in the side wall of the connector body, the housing being welded around its lower periphery to the support flange to form a fluid seal and to maintain the loading on the O-ring.
In accordance with features of a second embodiment, a flip-chip IC having solder bumps on its bottom surface is used and is soldered to pads of the first lobe section of the flexible circuit assembly preferably at the same time that selected electronic components and the terminals are soldered, as by a reflow operation, to circuit pads on the second lobe section disposed in the connector. Epoxy is then dispensed adjacent to the integrated circuit which flows underneath the IC and upon curing forms an improved bond between the flexible circuit assembly and the flip-chip IC die.
Additional objects, features and methods of the invention will be set forth in part in the description which follows and in part will be obvious from the description. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations and methods particularly pointed out in the appended claims.